A conventional flow controlling device has been developed that enables a simple interface from the outside to a setting device (a digital instrument, or the like) that sets the flow rate. As an example, there is a known flow controlling device for controlling and adjusting a valve in order to measure the flow of a fluid that is flowing in a flow path, and to control an adjusting valve through controlling means so that the flow of the fluid, which flows through the flow path, will match the flow that has been set. (See, for example, Japanese Unexamined Patent Application Publication 2000-205917 (Page 3 through Page 6, with Page 6 in Particular, and FIG. 1) (“JP '917”)).
Additionally, methods for setting the flow for the flow setting device include a method for accessing using analog signals and a method wherein a setting value is inputted using input keys that are provided on a setting device that is connected to the flow controlling device. There is also a method for sending the setting value from a personal computer that is connected so as to enable communications between the flow controlling device and the personal computer through an RS-485 cable, or the like. A conventional flow controlling device will be explained below for the case of the analog signals, one of the setting methods.
FIG. 2 is a structural diagram illustrating a first electric current route for a valve driving electric current of a flow controlling device used conventionally for controlling flow rates using analog signals. In FIG. 2, code 1 is a setting device for outputting, through multiple channels, analog signals (flow setting signals), in accordance with the flow rate that has been set. The operator is able to set the flow rate at will for each channel. Code 2 is a flow controlling device A, and 3 is a flow controlling device B. These flow controlling devices 2 and 3 are connected, in a plurality thereof and in a mutually non-isolated state, to each channel of the setting device 1. Each channel (CH1, CH2) of the setting device has a respective positive terminal (+) and negative terminal (−), and are connected together to enable conductance so that the negative terminals of each are at the same potential (that is, they are in a non-isolated state). While the flow controlling devices 2 and 3 will be explained below, because codes 2 and 3 have identical structures, the details will be explained for the flow controlling device A of code 2.
The flow controlling device A comprises a solenoid valve 10 for adjusting the opening of a flow path through which a gas, or the like, passes in this device, a valve driving circuit 11 for driving the solenoid valve 10, a microcomputer 12, as a controlling device for outputting an instruction signal to the valve driving circuit 11, and an analog inputting circuit 13 for receiving an analog signal from the setting device 1 and sending it to the microcomputer 12. It further comprises a first power supply circuit 14 and a second power supply circuit 15 which are supplied direct current electric power from the external power supply 4. Note that the microcomputer 12 is, for example, a single-chip microcomputer, comprising a CPU, a ROM, and a RAM (not shown) internally. Note that while, of course, the following structures (1) through (5) that are disclosed as the flow measuring device in JP '917, below, are provided in the flow rate measuring device A, for convenience in understanding the drawings, they are omitted from the drawings: (1) a flow path wherein a fluid flows; (2) a detecting element for detecting the flow of the fluid that is flowing in the flow path; (3) a signal processing circuit for processing a detection signal that is outputted from the detecting element; (4) a converting device for converting, into a digital signal, an analog signal that is outputted from the signal processing circuit; and (5) a calculating device for outputting the flow rate of the fluid that is flowing in the flow path, based on the digital signal outputted from the converting device. Additionally, the functions of these structures (1) through (5) are disclosed in JP '917 and are thus omitted in the descriptions.
Additionally, when a plurality of flow controlling devices for gases for, for example, burner combustion are used, the individual flow controlling devices 2 and 3 are connected to the analog output channels (CH1, CH2, . . . ) of the setting device 1, and a method is used wherein flow setting signals are sent to the respective flow controlling devices 2 and 3 from the setting device 1.
However, for reasons having to do with cost, many of the users of the setting device 1 use a type wherein there is no isolation between the individual output channels. In the conventional flow controlling device wherein the flow is set by an analog signal, or in JP '917 that uses this type of setting device 1, when connecting to the shared external power supply 4, the driving electric current from the valve driving circuit that drives the solenoid valve flows not only through the electric current route I1 illustrated by the dotted line in FIG. 2, above, but also flows through the electric current route I2, indicated by the double dotted line (where only one of polarity side of the power supply line is illustrated).
That is, when one focuses on the flow controlling device 2, when, in the setting device 1 the voltage is set to between 0 and 5 V, then, normally, an electric current of the order of only several dozen microamps flows into the analog inputting circuit 13 of the flow controlling device 2. However, the electric current that drives the solenoid valve is, at most, in the order of several hundred milliamps (mA). This valve driving electric current also flows through the setting device 1 and the flow controlling device 3 into the electric current route I2, illustrated by the double dotted line. When this happens, there is an effect on the signal of the analog inputting circuit 13, producing error also in the setting value that is inputted into the microcomputer 12. Furthermore, because the flow controlling device 2 normally operates so as to cause the flow to match the flow setting value, if there is a change in the setting value for the flow, or a change in the pressure of the gas that is supplied, then there will be a large change in the electric current for driving the valve, which means that the effect on the analog inputting circuit 13 will also vary.
Furthermore, FIG. 3 is a structural diagram showing the same structure as in FIG. 2, illustrating a second electric current route, and shows both the electric current route I1 and the electric current route I2 from when the flow controlling device 3 was considered. The valve driving electric current for the flow controlling device 3 flows also in the analog inputting circuit of this device 3, and this valve-driving electric current also flows into the analog inputting circuit 13 of the flow controlling device 2. The result is that the change in the valve driving electric current of the flow controlling device 3 produces a variation in the flow setting value for the flow controlling device 2. Furthermore, because changes in the valve driving electric current of the flow controlling device 2 has an effect also on the flow controlling device 3, so the flow controlling device 2 and the flow controlling device 3 interfere with each other, and the greater the number of connected flow controlling devices, the more the complex mutual interactions, which has a deleterious effect on the stability of the flow setting values, producing a problem with a deleterious effect on the stability of the controlled flow.
In order to solve this type of problem, one might consider just isolating the power supply circuits that provide the power supply to the analog inputting circuit or the valve driving circuit. While one might consider placing an isolator before the signal from the setting device is inputted into the analog inputting circuit in order to isolate the analog inputting circuit, this approach has the drawbacks that there will be error in the setting if the signal is not converted accurately, and that the cost is high. In contrast, in the method of isolating the power supply circuit, one may consider adding an isolating DC-DC converter to the power supply circuit. In this case, there is no problem even if there is a conversion error of several percent on the power supply side, and the approach of isolating the power supply circuit side is also better in terms of costs.
FIG. 4 is a structural diagram of the case wherein an isolating DC-DC converter is connected as, specifically, a third power supply circuit 16 to the power supply circuits of the flow controlling devices 2 and 3 in FIG. 2 and FIG. 3, above, where although this is technology relevant to the present invention, it is not yet known publicly. Note that the individual structures were explained in FIG. 2 and FIG. 3 above, so will be omitted in the explanation for FIG. 4. The solenoid valves 10 of the flow controlling devices 2 and 3 have different orifice diameters depending on the range of the flows controlled, and so will have different requirements for the driving forces, or in other words, will have different required maximum drive electric currents.
Here, in FIG. 4 wherein the third power supply circuit 16 (the isolating DC-DC converter) is connected to the flow controlling devices 2 and 3, the flow controlling devices 2 and 3 are in identical states, so here the explanation will focus on only the electric current route I2 in the valve driving circuit 11 of the valve controlling device 2. Here the electric current in the valve driving circuit 11 is first blocked at the C1 position, as with the electric current route I1, so that there is no flow directly into the external power supply 4. Additionally, the electric current route I2 attempts to flow through the analog inputting circuit 13 of the flow controlling device 2 and the setting device 1 into the analog inputting circuit 13 of the flow controlling device 3 as well, but because this electric current is blocked at the C2 position by the third power supply circuit 16 (the isolating DC-DC converter) of the flow controlling device 3, the interference between the flow controlling device 2 and the flow controlling device 3 due to this electric current, as explained using FIG. 2 and FIG. 3, is completely eliminated.
However, the flow controlling devices 2 and 3 require the use of a DC-DC converter with a capacity compatible with the maximum drive electric current of the solenoid valve 10, which will vary depending on the maximum flow of, for example, the gas flowing therethrough. In particular, if the flow controlling devices 2 and 3 are used for large flows, then a large driving electric current will be necessary because the orifice diameters will be large, requiring the use of a high-capacity DC-DC converter, which is costly and physically large. Because of this, there are a number of drawbacks, such as not being able to generalize the third power supply circuit 16 (DC-DC converter), and not being able to generalize the circuit board for mounting the third power supply circuit 16, the analog inputting circuit, the valve driving circuit, and the like.
The object of the present invention is to provide a flow controlling device capable of eliminating the interferences between flow controlling devices, even when connecting a plurality of flow controlling devices to a single setting device.